Untitled

184 MOLLUSCA FROM MIOCENE AND LOWER PLIOCENE OF VIRGINIA AND NORTH CAROLINA
but inconspicuous sutures. Nuclear whorls wanting.
Each of remaining turns sculptured with 4 approximately
equisized and equispaced spirals, very low,
broad, and straplike, mounted with close-set, squarish
tubercles, about 2 to each linear millimeter on the body
whorl; the foundation bands on the earlier whorls
almost or altogether obsolete, the tubercles sharper and
more rounded, thus lending a beaded aspect to the
sculpture of the posterior portion of the shell; a simple
secondary introduced on the penultima at the medial
line of the whorl, midway between the second and third
primaries, later becoming wavy and inconspicuously
beaded. Peripheral keel angular but not sharp, outlined
by a broad, simple, spiral band. Base flattened,
sculptured by strong, slightly rounded spirals varying
somewhat in width and spacing, tending to become
stronger and more distant in the umbilical region; interspaces
sculptured with radiating incrementals.
Aperture badly broken, probably angular, broader than
it is high. Pillar smooth, concave, strengthened by
the reflected callus. Umbilicus imperforate.
The species, though described from a unique type,
is sharply separated from all other forms of this
area by the monotonous pyramidal outline, unbroken
by any angula-rities or convexities of the whorls and
by the 4 rather than 3 primary spirals upon the adolescents
and the squarish tubercles which adorn the adult
spirals. Among the Recent species, its nearest kin is
perhaps Oalliostoma apicinwm Dall of the West Indian
fauna, a slightly smaller, more elevated conch with a
much finer, sharper sculpturing.
Dimensions of holotype: Height 11.1 mm., maximum
diameter 10.0 mm.
Holotype: U.S.N.M. 325470.
Type locality: Eight to 9 miles southeast of Greenville,
Pitt County, N. C. Yorktown formation, zone 2.
In the Oalliostoma philanthropum group, including
the subspecies pontoni Mansfield (pl. 26, fig. 15) and 0.
basicwm Dall (pl. 26, fig. 11), a guide fossil of zone 2
of the Yorktown formation in Virginia and North
Carolina, 0. mitchelli (Conrad) (pl. 26, figs. 19, 23), and
0. ruffinii (H. C. Lea) (pl. 26, fig. 18), the posterior
suture is overhung by the beaded peripheral keel of the
preceding whorl. The group is further removed from
0. cheopsi by the 3 primary spirals on the early whorls
and by the sharp well-rounded beads of the adult ornamentation.
Distribution: Yorktown formation, 8 to 9 miles southeast of
Greenville, Pitt County, N. C.
Calliostoma carolinense Gardner, n. sp.
Plate 26, figures 3, 4
Shell heavy, moderately low; the regularity of the
pyramidal outline broken by the strong spiral cording.
Whorls narrowly tabulated, 6 in number, including the
protoconch, which is very small, probably of not more
than one turn, and, in its decorticated condition, not
readily differentiated from the conch. Initial sculpture
on the conch of 3 spiral lirae, equal in size and
spacing; a fourth spiral introduced on the next to the
last whorl of the spire between the posterior and medial
lirae, increasing somewhat in strength and persistent
but not attaining the prominence of the original primaries;
no other lirae intercalated: on adult whorls
original posterior primary outlining the shoulder; the
anterior, together with the stronger .outer basal spiral,
forming the double peripheral keel; and the medial
of the 3 original spirals, together with a fourth, symmetrically
disposed between the peripheral and shoulder
spirals. Base flattened, heavily sculptured with 4
additional broad straplike cords extending far within
the aperture, separated by interspaces of approximately
their own width; umbilical keel outlined by a similar
spiral. Incremental sculpture microscopically fine.
Suture distinct but not conspicuous, following the anterior
of the peripheral cords, which is commonly partially
visible as a thin, sharp thread directly behind the
suture.
Aperture transversely ovate. ·Outer margin imperfect,
crenulated by the strong spirals. Parietal wall
thinly glazed. Columellar margin concave, simple, reflected.
Umbilical region excavated but not perforate.
Dimensions of holotype: Height 9.8 mm., maximum
diameter 11.2 mm.
Holotype: U.S.N.M. 325472.
Type locality: Hamilton Bluff on the Roanoke River,
Martin County, N.C. Yorktown formation, zone 2.
0 alliostoma carolinense is characterized by the prominence
of the primaries and the reduced number ·of the
secondaries. It is, apparently, an end member of the
0. virginicwm group.
Oalliostoma harrisianrum Olsson, 1916, seems from the
description and the rather poor illustration to be intermediate
between 0. carolinense and 0. virginicum
s. s. In 0. carolinense the regularity of the profile is
broken by the heavy spirals, but the profile of 0. harrisianum
more closely resembles that of 0. virginicum.
The number of spirals is more reduced in 0. carolinense
than it is in either of the two species from Virginia and,
with the possible exception of the peripheral spirals,
they seem to be stronger than those of 0. harrisia1'1ffJJm.
The North Atlantic species Oalliostoma occidentale
Mighels and Adams, 1842, is similar in general aspect,
but the 3 primary spirals are beaded on the juvenile
shells, and the sculpture on the base of the adult is irregular
and tends to become obsolete except toward the
periphery and the umbilical area.
Distribution: Yorktown formation, Hamilton Bluff on the
Roanoke River, Martin County, N. C.